A generic Direction Finding (DF) system consists of four major components: the antenna system, the receiver, one or more processors and the control/output system. The antenna system must address the contradictory requirements of both an omnidirectional pattern that permits reception over the widest possible field of view, and a "pencil beam" that permits great accuracy in determining the angle of arrival of an intercepted signal. These conflicting requirements cannot be met with a single static antenna. Resort, therefore, is often made to the use of an antenna array, a spinning narrow-band pattern antenna, or a phased array (an antenna capable of rapidly altering its radiation pattern by electronic means). One major problem with the spinner type of DF antenna is that once it locks onto a target, it is blind to the rest of the field of view. Phased array antennas have the disadvantage of requiring an assortment of expensive electronics to conduct the electronic beam scanning.
The fundamental trade-off between instantaneous field of view and time available for an observation is a design consideration of any DF system. Even an antenna with a modest field of view can be used to provide 360 degree coverage in a direction finder by rotating the antenna. However, rotating the antenna poses problems when dealing with frequency-agile emission or signals of short duration. The mean time required to intercept a signal and the duration of the signal being sampled critically depend upon the coincidence of the transmitting antenna pattern, which may also be turning, and the rotating DF antenna. It is such trade-offs that make the design of an effective DF system a challenge.
Previous attempts at designing such an antenna have all had various problems such as low gain, limited operational bandwidth, excessive size and weight, low angle of arrival (AOA) accuracy, and limited azimuthal field of view once a target is acquired. Some previous antenna designs have used low-gain dipole or spiral antenna elements. These designs offer simultaneous field of view coverage, but suffer from limited bandwidth and low AOA accuracy. Other antenna designs have larger bandwidths, but do not offer simultaneous coverage over the entire field of view.